Here's a list of games and their rox/xp balances. At the end of the day is personal preferences. But it's known the "Play for rox" on The Great Beanstalk is the best for xp and Ice Scream is the best for rox (you might get a hand cramp tho, play at own risk)

Blutterby Field :

•  60 score will give you 10 rox and 4 exp.
• 202 score will give you 34 rox and 14 exp.
•  455 score will give you 77 rox and 32 exp

 

Ice-Scream :

•  137 score will give you 52 rox and 22 exp.
• 209 score will give you 79 rox and 33 exp.
• 403 score will give you 153 rox and 64 exp.

 

Moshling Boshling :

• 1 score will give you 10 rox and 3 exp.
• 2 score will give you 20 rox and 7 exp.
• 3 score will give you 30 rox and 10 exp.

 

Quack Attack :

• 13 score will give you 5 rox and 3 exp.
• 60 score will give you 24 rox and 12 exp.
• 160 score will give you 64 rox and 32 exp.

 

Bug Rush :

• 19 score will give you 17 rox and 7 exp.
• 29 score will give you 26 rox and 10 exp.
• 41 score will give you 37 rox and 14 exp.

 

Shouty Shack :

• 5 score will give you 5 rox and 2 exp.

 

The Great Moshi Beanstalk : 

• 5000 score will give you 30 rox and 13 exp.
• 6711 score will give you 40 rox and 17 exp.
• 10000 score will give you 60 rox and 25 exp.

 

The undergroup disco :

• 17 score will give you 22 rox and 14 exp.
• 22 score will give you 29 rox and 18 exp.
• 22 score will give you 29 rox and 18 exp.

 

Thump Glump :

• 700 score will give you 11 rox and 4 exp.
• 5000 score will give you 75 rox and 25 exp.
• 9000 score will give you 135 rox and 45 exp.

 

En-Gen :

• 4000 score will give you 44 rox and 16 exp.
• 6000 score will give you 66 rox and 24 exp. 
• 13450 score will give you 148 rox and 54 exp.